Timing of vaccinations in premature infants.

Preterm infants have immunological immaturities that may impact on vaccine responses. Larger premature infants mount immune responses to vaccines that are similar to those of full term infants, but very premature infants (<30 weeks' gestation at birth) have specific defects in vaccine responsiveness. The immunogenicity of diphtheria, tetanus and pertussis antigens is similar in full term and premature infants. Poliovirus vaccines, however, do not always stimulate adequate antibody responses in premature infants. The immunogenicity of Haemophilus influenzae type b conjugate vaccines varies widely in studies of premature infants, and may be affected both by choice of conjugate protein and by the infant's overall health. Hepatitis B vaccine given at birth appears poorly immunogenic in infants with birthweights <1750g, with delay in the administration of the first dose yielding improved immunogenicity. Sick premature infants may suffer increased episodes of apnoea following vaccine administration. Persistence of immunity, the quality of the immune response, and evaluation of the specific tolerability and immunogenicity of new vaccines in premature infants are topics needing further research. Although it is generally true that recommendations for vaccination of term infants are applicable to premature infants, it is not always specifically true. Optimal care of preterm infants requires attention to the exceptions to this generalisation.